1. Field of the Invention
The present invention pertains to lubrication systems for lubricating the bearings of rotating equipment. More specifically, the present invention is directed to an oil mist lubricating system in which major operating variables of the system are controlled by a microprocessor.
2. Description of the Prior Art
Oil mist lubrication is used in many industries to provide continuous, effective lubrication to anti-friction bearings in rotating equipment such as centrifugal pumps, electric motors, steam turbines, gear boxes, blowers and fans. An oil mist lubrication system typically comprises a generator in which a compressed air stream in turbulent flow is combined with a liquid lubricant to create a fine mist of oil particles suspended in an air stream. These oil particles are typically one to five microns in diameter. The oil mist is transported through a piping system and delivered into the bearing housings of one or more pieces of rotating equipment. The oil mist continuously bathes the bearings of the equipment and maintains a slight positive pressure in the bearing housing to reduce contamination from outside sources. If the lubricating system functions properly, bearing life is extended, equipment down time and maintenance costs are reduced.
Optimum operation of an oil mist system requires that equipment bearings receive a reliable, continuous supply of lubricant while minimizing two important variables: the amount of oil consumed and the amount of spray mist escaping to the outside environment. When oil mist is generated, the oil is atomized into very fine particles and can be conveyed long distances in a properly designed header system with minimum wetting out on the walls of the pipe in which it is being conveyed. These fine particles, referred to as "dry mist", must be converted into larger particles, known at "wet mist", in order to wet out on the metal surfaces of the equipment bearings being lubricated. This is accomplished by passing the mist through a specially designed restriction orifice known as a reclassifier. The reclassifier induces turbulence in the stream to convert small particles into larger ones before the mist enters the equipment bearing housing. These reclassifiers serve the additional purpose of metering the amount of lubricant to each bearing to avoid over or under lubricating. Selection of the correct reclassifier for each application point in the system is based upon an understanding of the exact bearing configuration for each piece of equipment to be lubricated. Some of the oil mist particles, particularly the smallest ones, do not wet out on the metal surfaces of the equipment being lubricated. Instead, they pass through the bearing housings and are vented to the atmosphere. Thus, supplying sufficient oil without over consumption and minimizing stray mist contamination of the environment are problems not sufficiently addressed by the prior art.
Most integrated lubricating systems include an inlet air supply, an input oil supply, a mist generating head and controls for adjusting and monitoring the operation of the system and the operating variables thereof. Oil mist systems of the prior art, in recent years, have utilized analog controls. Such systems are designed to provide an alarm when one of the operating variables moves outside of an operating range set when the system is constructed. These ranges may be quite wide. For example, oil temperature in the mist unit reservoir is typically set at a minimum of 80 degrees F. and a maximum of 140 degrees F. This provides the minimum level of control to assure that the equipment is being adequately lubricated but it provides no opportunity to optimize the system operation. Another shortcoming of prior art oil mist systems is that an alarm condition in one variable might be accompanied by one or more alarms for other variables. For example, an alarm condition on a low mist pressure will often be accompanied by an alarm for low air temperature because the control system is designed to shut off the air heater when air flow decreases. An operator looking at a control panel when two or more alarm conditions are identified would not immediately know which condition was at fault and which ones were secondary alarms. While lubricating systems of recent years are much improved, a number of shortcomings still exist, leaving room for improvement.